Frequency-division duplexing in a time-division duplexing mode for a telecommunications system

ABSTRACT

Certain features relate to operating a distributed antenna system or repeater system communicating frequency-division duplexing (“FDD”) signals in a time-division duplexing (“TDD”) mode. A TDD mode scheduler is configured for monitoring a downlink communications channel for the start of a downlink frame, sub-frame, or resource slot. Based on the start of a downlink frame, sub-frame, or resource slot, the TDD mode scheduler can identify a TDD transmission time-slot. The TDD mode scheduler can schedule high-powered downlink sub-frames during the TDD transmission time-slots where higher power output may be desirable. Based on the indication of the TDD transmission time-slot, a transmit/receive controller can increase the gain of the downlink communication and reduce the gain of the uplink communication.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a U.S. National Stage Application of PCT ApplicationSerial No. PCT/US2015/024740, filed Apr. 7, 2015, and titled“FREQUENCY-DIVISION DUPLEXING IN A TIME-DIVISION DUPLEXING MODE FOR ATELECOMMUNICATIONS SYSTEM”, which claims the benefit of U.S. ProvisionalApplication Ser. No. 61/978,299, filed Apr. 11, 2014 and titled“Frequency-Division Duplexing in a Time-Division Duplexing Mode for aTelecommunications System,” the contents of all of which areincorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to telecommunications systemsand more particularly (although not necessarily exclusively) todistributed antenna systems that can perform frequency-divisionduplexing communications in a time-division duplexing mode.

BACKGROUND

A distributed antenna system (“DAS”) can include one or more head-endunits and multiple remote units coupled to each head-end unit. A DAS canbe used to extend wireless coverage in an area. Head-end units can becoupled to one or more base stations. A head-end unit can receivedownlink signals from the base station and distribute downlink signalsin analog or digital format to one or more remote units. The remoteunits can transmit the downlink signals to user equipment devices withincoverage areas serviced by the remote units. In the uplink direction,signals from user equipment devices may be received by the remote units.The remote units can transmit the uplink signals received from userequipment devices to the head-end unit. The head-end unit can transmituplink signals to the serving base stations. Often, strong signals atthe downlink path can interfere with incoming signals at the uplinkpath. It may be desirable to minimize the interference between downlinkand uplink paths in a DAS.

Remote units can operate in a network that radiates frequency-divisionduplexing (“FDD”) signals. In an FDD network, remote units and repeaterscan use transmit/receive duplexers or filter stages to protect receivedsignals in a receiving communications path from interference caused bysignals other than the received signals. But, duplexers and filters donot allow for frequency agnostic, radio frequency front-ends unlesssignificant limitations are introduced through transmit and receiveantenna isolation.

SUMMARY

In one aspect, a distributed antenna system is provided. The distributedantenna system can include a head-end unit including a time-divisionduplexing (“TDD”) mode scheduler. The TDD mode scheduler is configuredto identify a start of a downlink radio block that includesfrequency-division duplexing (“FDD”) signals based on monitoring adownlink communications channel and generate an indication of a TDDtransmission time-slot based on the start of the downlink radio block.The distributed antenna system can also include a remote unit configuredto receive an uplink radio block that includes FDD signals on an uplinkcommunications channel and transmit the downlink radio block on thedownlink communications channel. The remote unit can also include atransmit/receive controller. The transmit/receive controller isconfigured to receive the indication of the TDD transmission time-slot.The transmit/receive controller is also configured to increase adownlink gain of the downlink radio block during the TDD transmissiontime-slot and reduce an uplink gain of the uplink radio block during theTDD transmission time-slot.

In another aspect, a unit of a repeater system is provided. The unit caninclude a transmitter configured to transmit a downlink radio block thatincludes downlink FDD signals on a downlink communications channel and areceiver configured to receive an uplink radio block that includesuplink FDD signals on an uplink communications channel. The unit canalso include a TDD mode scheduler configured to identify a start of thedownlink radio block based on monitoring a downlink communicationschannel and generate an indication of a TDD transmission time-slot basedon the start of the downlink radio block. The unit can also include atransmit/receive controller configured to receive the indication of theTDD transmission time-slot, increase a downlink gain of the downlinkradio block during the TDD transmission time-slot, and reduce an uplinkgain of the uplink radio block during the TDD transmission time-slot.

According to another aspect, a method is provided. The method caninclude monitoring a downlink communications channel in whichinformation formatted in radio blocks that include FDD signals iscommunicated. The method can further include identifying, based on thedownlink communications channel, a start of a downlink radio block. Themethod can also include, based on the start of the downlink radio block,generating an indication of a TDD transmission time-slot. The method canalso include increasing a downlink gain of the downlink radio blockduring the TDD transmission time-slot and reducing an uplink gain of anuplink radio block during the TDD transmission time-slot.

These illustrative aspects and features are mentioned not to limit ordefine the disclosure, but to provide examples to aid understanding ofthe concepts disclosed in this application. Other aspects, advantages,and features of the present disclosure will become apparent after reviewof the entire application.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting an example of a base station and adistributed antenna system (“DAS”) suitable for performingfrequency-division duplexing (“FDD”) communications in a time-divisionduplexing (“TDD”) mode according to one aspect of the presentdisclosure.

FIG. 2 depicts an example of a radio frame format suitable for radiatingFDD mobile-network signals in a TDD mode according to one aspect of thepresent disclosure.

FIG. 3 is a block diagram showing an example of a remote unit of FIG. 2,configured for radiating FDD mobile-network signals in a TDD mode andhaving a shared transmit-receive antenna according to one aspect of thepresent disclosure.

FIG. 4 is a block diagram showing an example of a remote unit of FIG. 2,configured for having separate transmit and receive antennas suitablefor radiating FDD mobile-network signals in a TDD mode according to oneaspect of the present disclosure.

FIG. 5 is a block diagram showing an example of the DAS of FIG. 1configured for radiating FDD mobile network signals in a TDD modeaccording to one aspect of the present disclosure.

FIG. 6 is a flow chart depicting an example of a process for using a DASconfigured for FDD communications in a TDD mode.

DETAILED DESCRIPTION

Certain aspects and features relate to transporting frequency-divisionduplexing (“FDD”) signals or signal information in a time-divisionduplexing (“TDD”) mode for a telecommunications system. For example, ahead-end unit or a remote unit of a distributed antenna system (“DAS”)can transport FDD signals in a TDD mode and can schedule higher powertransmissions, increase power to the downlink signal during transmissiontime slots, and decrease uplink gain during transmission time slots toobtain desirable signal isolation. The reduction of the uplink receivergain stages can be high enough to avoid uplink performance degradationdue to receiver overdrive and interference from downlink signalscoupling into the uplink receiver chain. Transporting FDD signals in aTDD mode can allow for a frequency agnostic front-end for a DAS in whichremote units can transmit and receive network signals simultaneously inmultiple frequency bands while minimizing the amount of hardwarerequired.

According to one example, performing FDD in a TDD mode can beimplemented using a TDD mode scheduler and a transmit/receive (“TX/RX”)controller. The TDD mode scheduler can be located, for example, at aremote unit in a DAS. The TDD mode scheduler can identify transmitframes or transmit sub-frames in a communications channel (e.g., theframes and sub-frames pertaining to downlink activity). The TDD modescheduler can schedule high-power downlink sub-frames by informing aTX/RX controller of the TDD transmission time-slots. The TX/RXcontroller can also be located, for example, at a remote unit in theDAS. The TX/RX controller can receive indications of the TDDtransmission time-slots, and, in response, increase power to thehigh-power downlink sub-frames and reduce the downlink signal power whenincoming uplink sub-frames are scheduled from distant mobiles. Reducingthe uplink receiver chain gain for uplink sub-frames can furtherminimize interference caused by increasing the power to the downlinksub-frames. When the uplink receiver chain gain is reduced it is stillpossible to receive the uplink transmissions of mobiles that are locatedclose to the remote unit or of mobiles that are transmitting at high RFpower.

According to certain aspects, performing FDD communications in a TDDmode can protect the receivers in remote units from being overdriven bystrong transmit signals while minimizing the amount of hardware used forprotection. For example, certain aspects and features can help eliminateextra hardware, such as filter-based duplexers that are configured forfixed frequency bands, reducing the overall complexity of the system.

Additionally, certain aspects and features can help avoid limitations inisolation levels between transmitter and receiver antennas caused byenvironmental conditions. For example, environments with highscattering, such as in-building areas, can degrade antenna isolationlevels and further limit radio frequency (“RF”) transmit power toundesirable values (e.g., below 20 dB). Transporting FDD signals in aTDD mode can allow for a frequency agnostic front-end that can adapt tovarious environmental conditions dynamically. For example, according toone aspect of the present disclosure, the uplink front-end gain can bereduced by 1 dB or more (e.g., 10 dB or even switched off completely)when transmitting high-power downlink sub-frames. The amount ofreduction in uplink front-end gain can vary depending on the isolationbetween the transmit path and receive path measured at a remote unit.

As new wireless communications standards are introduced or adopted,certain aspects and features of a frequency agnostic RF front-endoperating in a TDD mode can provide advantages over fixed-filtersolutions. A frequency agnostic front-end can allow for the transmitpath and receive path of the DAS remote unit to be retuned for new ordifferent frequency bands, as desired. As a result, a frequency agnosticfront-end can minimize the number of remote unit variants associatedwith different wireless communications standards.

According to another aspect of the present disclosure, operating in theTDD mode allows for FDD-based devices in the DAS to continue to operatein FDD mode.

Detailed descriptions of certain examples are discussed below. Theseillustrative examples are given to introduce the reader to the generalsubject matter discussed here and are not intended to limit the scope ofthe disclosed concepts. The following sections describe variousadditional aspects and examples with reference to the drawings in whichlike numerals indicate like elements, and directional descriptions areused to describe the illustrative examples but, like the illustrativeexamples, should not be used to limit the present disclosure.

FIG. 1 depicts an example of a DAS 100 suitable for performing FDD in aTDD mode according to aspects and features of the subject matterdescribed herein. The DAS 100 can include a network of spatiallyseparated remote units 102 a-d communicatively coupled to a head-endunit 104 for communicating with a base station 106 according to oneaspect. For example, remote units 102 a-d can connect directly to thehead-end unit 104. In other aspects, the head-end unit 104 can becoupled to remote units 102 a-d via a transport expansion unit oranother intermediate device. The remote units 102 a-d can providewireless service to user equipment devices positioned in respectivegeographic coverage zones 110, 112.

The head-end unit 104 can receive uplink downlink signals from the basestation 106 and transmit uplink signals to the base station 106. Anysuitable communication link can be used for communication between basestations and head-end units, such as (but not limited to) a directconnection or a wireless connection. A direct connection can include,for example, a connection via a copper, optical fiber, or other suitablecommunication medium. In some aspects, the head-end unit 104 can includean external repeater or internal RF transceiver to communicate with thebase station 106. In some aspects, the head-end unit 104 can combinedownlink signals received from different base stations. The head-endunit 104 can transmit the combined downlink signals to one or more ofthe remote units 102 a-d.

Remote unit 102 a can provide signal coverage in a coverage zone 110 bytransmitting downlink signals to mobile communication devices in thecoverage zone 110 and receiving uplink signals from the user equipmentin the coverage zone 110. In another aspect, multiple remote units 102b-d can provide signal coverage in a single coverage zone 112. Theremote units 102 a-d can transmit uplink signals to the head-end unit104. The head-end unit 104 can combine uplink signals received fromremote units 102 a-d for transmission to the base station 106.

The information on the signals transmitted and received by remote units102 a-d and head-end unit 104 can be grouped in a radio frame formatsuitable for radiating FDD mobile network signals in a TDD mode. FIG. 2depicts an example of a radio frame format according to certain aspectsand features. While the radio frame format depicted in FIG. 2 includesan LTE (E-UTRA) type 1 frame structure, other radio frame formats canalso be used. The radio frame includes twenty resource slots labeled0-19. Resource slots can be grouped into pairs to create ten sub-frameslabeled 0-9. For example, sub-frame 0 includes slots 0 and 1, sub-frame1 includes slot 2 and 3, etc. Each resource slot or “block” can includeseven symbols labeled symbols 0-7. Radio frame formats can containvarious frame, sub-frame, and slot timing durations. In one example, aradio frame 10 ms in duration can consist of ten sub-frames 1.0 ms induration each. Each sub-frame can contain two resource slots of duration0.5 ms each. FDD mobile network signals transmitted in a radio framestructure can be divided into uplink and downlink signals and grouped inradio frames, sub-frames, and resource slots in various configurations.For example, downlink network signals can be communicated in sub-frames0, 2, 4, 6, and 8 and uplink network signals can be communicated insub-frames 1, 3, 5, 7, and 9 in a radio frame that includes 10sub-frames. In another example, downlink network signals and uplinkmobile network signals can be communicated in alternate radio frames.The time duration of each downlink transmission can be referred to as aTDD transmission time-slot, which can correspond to the duration of theframe, sub-frame, or resource slot containing the downlink signal. Forexample, if downlink signals are communicated in sub-frames 0, 2, 4, 6,and 8 in a 10 ms radio frame, then the TDD transmission time-slots canbe 0.5 ms in duration each.

Each TDD time-slot can correspond to a duration of time in which highpowered downlink signals can be scheduled. In performing FDDcommunications in a TDD mode, remote units and head-end units canincrease the power applied to transmit frames, sub-frames, or resourceslots (hereinafter collectively referred to as “radio blocks”) duringTDD transmission time-slots. To reduce signal interference at thereceiver, remote units and head-end units can reduce the gain ofincoming, received radio blocks during TDD transmission time-slots.

Remote units 102 a-d and head-end unit 104 in DAS 100 can monitor adownlink communications channel to identify the TDD transmissiontime-slots that correspond to a downlink radio block in order to operatein a TDD mode. Remote units 102 a-d and head-end unit 104 can beconfigured in various ways in order to monitor radio frames and radiateFDD network signals in a TDD mode. FIGS. 3-5 depict examples of certainconfigurations.

FIG. 3 is an example of a schematic block diagram of a DAS 100 in whichthe head-end unit 104 is communicatively coupled to the remote unit 102d. The head-end unit 104 can transmit downlink signals to the remoteunit 102 d via a downlink signal path and can receive uplink signalsfrom the remote unit 102 d via an uplink signal path. Head-end unit 104can include a TDD mode scheduler 304, which monitors a downlinkcommunications channel for the start of a TDD transmission time-slot ina radio frame. The length of a frame can be determined by the format ofthe frame and may be known to TDD mode scheduler 304 that is monitoringa downlink communications channel. The TDD mode scheduler 304 canidentify the start of a downlink radio block and use the start of thedownlink radio block to identify a TDD transmission time-slot within thecommunications channel. The TDD mode scheduler 304 can generate anindication of the TDD transmission time-slot and communicate theindication to a TX/RX controller 306 located in the remote unit 102 d.

The indication of the TDD transmission time-slot can include informationspecifying the start time and end time of the radio block that containsthe downlink transmission. Alternatively, the indication can includeinformation specifying the total duration of the radio block thatcontains the downlink transmission.

The remote unit 102 d can include the TX/RX controller 306, signalconditioners 308, 310, and a coupling matrix 312 coupled to an antenna314. The TX/RX controller 306 can detect incoming TDD transmissiontime-slots from the TDD mode scheduler 304 and increase the powerapplied to the downlink radio block. In order to minimize signalinterference, the TX/RX controller 306 can also reduce the power of anyincoming uplink radio blocks during the TDD transmission time-slot. Insome aspects, the TX/RX controller 306 can increase and reduce the gainof radio blocks through the use of the signal conditions 308, 310.Increasing the transmit power level may include increasing the powerenvelope of the sub-frame rather than the power envelope of the actualresource blocks. According to another aspect of the present disclosure,the transmit power level can be increased on a per-slot basis. Accordingto one further aspect of this invention the TX/RX controller 306 canalso reduce the power of a downlink radio block during a time slot notmarked as a TDD transmission.

Signal conditioner 310 can be located in the uplink path and signalconditioner 308 can be located in the downlink path. Each signalconditioner 308, 310 can be coupled to the TX/RX controller 306 and tothe coupling matrix 312. Signal conditioners 308-310 can includeattenuators, variable gain amplifiers, switches, relays, or otherelements, such as multipliers or digital signal scalers, used in digitalsignal processing. The signal conditioner 308 can adjust the gain of thedownlink resource block via a command from the TX/RX controller 306.Similarly, the signal conditioner 310 can adjust the gain of the uplinkresource block via a command from the TX/RX controller 306. TX/RXcontroller 306 can be a controller or logic circuit that receivesinstructions from the TDD scheduler 304 and communicates with signalconditioners 308 and 310 via serial or parallel interfaces. The signalconditioners 308, 310 can communicate signals to and from the couplingmatrix 312. The coupling matrix 312 can include a three-port deviceconfigured to combine the transmit path output (downlink), the receivepath input (uplink) and the transmit/receive signals from the antenna314. The coupling matrix 312 can include, for example, a circulator,combiner, isolator, or other suitable device for processing radiofrequency signals.

According to one aspect of the present disclosure, the TDD modescheduler 304 can be configured to schedule radio blocks for distantuser devices in the time periods of the high-power downlink sub-frames.The DAS remote unit 102 d and other remote units adjacent to head-endunit 104 can be scheduled to apply the high-power mode to differentsub-frames to minimize interference. For example, if remote unit 102 dis transmitting at a higher power, the TDD mode scheduler 304 caninstruct a different, adjacent remote unit to adjust to operate at alower power to minimize interference and maximize data throughput formobiles that are located at similar distances from remote unit 102 d andother adjacent remote units.

High-power downlink scheduling can be performed dynamically based oninformation received from a DAS remote unit, traffic conditions, or adistance distribution of the user devices served by the DAS. Schedulingof radio blocks can also be changed dynamically according to trafficneeds. For example, mobile user devices located at an edge of a cell mayuse more high-power slots.

According to another aspect of the present disclosure, along withmonitoring a downlink communications channel, the TDD mode scheduler 304can be configured to monitor an uplink communications channel in orderto detect uplink traffic and activity. For example, adjacent userequipment devices transmitting uplink signals on the same frequency bandcan cause interference and signal degradation. The TDD mode scheduler304 can analyze the signal frequency spectrum used by user devices anduse the detected uplink activity information to further optimize andassign high- power downlink sub-frames. The TX/RX controller 306 canadjust the transmit power level of the downlink sub-frames and uplinksub-frames during the times high-power downlink sub-frames arescheduled.

FIG. 4 is a block diagram showing another example configuration for aremote unit in DAS 100 suitable for radiating FDD mobile network signalsin a TDD mode. Remote unit 102 b can include a TDD mode scheduler 404communicatively coupled with a TX/RX controller 406. Similar to the TDDmode scheduler 304, the TDD mode scheduler 404 in remote unit 102 b canmonitor a downlink communications channel for the start of a TDDtransmission time-slot in a radio frame and communicate an indication ofthe TDD transmission time slot to the TX/RX controller 406.

The TX/RX controller 406 can be coupled to signal conditioners 408, 410.Signal conditioners 408, 410 can adjust the gains of downlink and uplinkcommunications radio blocks according to commands from the TX/RXcontroller 406. Signal conditioners 408,410 can be communicativelycoupled to a coupling matrix 412 coupled to a shared TX/RX antenna 414.The shared TX/RX antenna 414 is configured to both transmit and receivesignals between the remote unit 102 b and one or more user equipmentdevices.

FIG. 5 is an example of remote unit 102 c having separate transmit andreceive antennas 514, 516 suitable for radiating FDD mobile networksignals in a TDD mode. Similar to the remote units 102 b, 102 d, theremote unit 102 c can include a TDD mode scheduler 504 coupled to aTX/RX controller 506 coupled to signal conditioners 508, 510. The signalconditioners 508, 510 can be coupled to a coupling matrix 512. Incontrast to the shared TX/RX antenna discussed above with respect toFIG. 4, the DAS remote unit 102 c can include separate antennas fortransmitting and receiving signals. The coupling matrix 512 can becoupled to the separate TX/RX antennas 514, 516. In some examples,circulators or couplers can be cascaded to improve the isolation betweenthe receiving and transmitting antennas. In other aspects, however, thetransmit antenna 514 can be coupled directly to the transmit path andthe receive antenna 516 can be coupled directly to the receive path. Byusing separate antennas, isolation values 40 dB or more can be achieved.Cross-polarization of the two antennas 514, 516, spatial separation, orany nulling of the electro-magnetic field of the signal of the transmitantenna 514 at the position of the receive antenna 516 can improve theisolation level.

Additionally, when separate antennas 514, 516 are used at the remoteunit 102 c, transmit to receive isolation can be determined by measuringthe isolation between transmit antenna 514 and the receive antenna 516as a function of frequency. Measured isolation levels can be used todetermine an uplink gain reduction that can further reduce signaldegradation at the downlink communications path. The TX/RX controllers506 can determine isolation levels by calculating the amount of powertransmitted on the transmit path that is received on the receive pathfor each frequency.

By using the measured isolation levels, the amount of uplink front-endgain reduction can be determined by the following relationship:

Isolation_required=Isolation_measured (f)−ΔP_tx (f)−Δ_G_rx (f)

Where:

-   -   Isolation_required is the isolation that the remote unit        front-end needs for simultaneous operation of receive and        transmit functions with no degradation of the receive path, with        ΔP_tx (f)=0 and ΔG_rx (f)=0. Isolation_measured (f) is the        measured transmit to receive isolation depending on the        frequency.    -   ΔP_tx (f) is the change of transmit power within the high power        downlink sub-frames compared to the nominal power. A ΔP_tx        (f)=+10 dB represents an increase of the output power of 10 dB.        The change in the transmit power can be achieved by changing the        gain in the transmit path.    -   ΔG_rx (f) is the change of DAS remote unit front-end gain        compared to the nominal gain for regular downlink power. A ΔG_rx        (f)=−10 dB represents a reduction of the front-end gain of the        receiver by 10 dB.

According to a further aspect of this invention the systems depicted inFIG. 4 and FIG. 5 are not necessarily limited to a remote unit in a DASsystem but can represent the part of a repeater system providingcoverage where the repeater system uses an over the air link to the basestation.

FIG. 6 is a flow chart depicting an example of a process for using a DASin a TDD mode for an FDD mobile network system according to an aspect ofthe present disclosure.

In block 600, a component in a DAS, such as a head-end unit or a remoteunit, can monitor a downlink communications channel in which informationformatted in radio blocks is communicated. For example, remote units 102a-d or head-end unit 104 can include a TDD mode scheduler, such as oneof the TDD mode schedulers 304, 404, 504, that can monitor the downlinkcommunications channel. Various configurations for monitoring thedownlink communications channel are possible. For example, the TDD modescheduler can be communicatively coupled to the downlink communicationslink from the head-end unit such that information sent on the downlinkcommunications link is also input into a network interface on the TDDmode scheduler. Alternatively, signals on the downlink communicationschannel can be input into a processor, such as a field programmable gatearray or a dedicated baseband processor in the TDD mode scheduler. TheTDD mode scheduler can continually process the downlink communicationsignal via a network interface or processor to analyze the type ofinformation on the path (e.g., whether the information is a transmissionframe, sub-frame, or resource slot).

In block 602, based on the downlink communications channel, a start of adownlink radio block is identified. For example, one of the TDD modeschedulers 304, 404, 504 can identify the start of the downlink radioblock by processing the information on the downlink channel andsearching for an identifier or reference data in the information thatcharacterizes the radio block as a downlink radio block or an uplinkradio block. Alternatively, the TDD mode scheduler can processinformation on the downlink communications path to search for controlinformation that can specify scheduling assignments for downlink radioblocks and uplink radio blocks. The TDD mode scheduler can utilize thescheduling assignment control information to identify the start of adownlink radio block detected in a subsequent communication in thedownlink path. Other forms of identifying the start of the downlinkradio block are also possible.

In block 604, based on the start of the downlink radio block, anindication of a TDD transmission time-slot is generated. For example,one of the TDD mode schedulers 304, 404, 504 can generate an indicationof a TDD transmission time slot. In one aspect, the length of thedownlink radio block may be known by the TDD mode scheduler. Uponreceiving the start of the downlink radio block, a processor in the TDDmode scheduler can calculate the duration for the downlink radio block.The TDD mode schedule can subsequently generate an indication via asignal including information specifying the duration information of theTDD transmission time-slot. In another aspect, the TDD mode schedulercan generate an indication via a signal including detailed informationpertaining to the downlink radio block. For example, in the indication,the TDD mode scheduler can specify the total duration of the radioframe, the start time of the downlink radio block, and the end time ofthe downlink radio block. The TDD mode scheduler can also generate anindication of a TDD transmission time-slot in any other form thatcommunicates the location and duration of the downlink radio blockwithin the radio frame. The indication can include a digital signalincluding a binary string of 1s and 0s. Alternatively, the indicationcan include a radio frequency carrier wave containing analog informationassociated with the TDD transmission time-slot.

In block 606, a downlink gain of the downlink radio block is increasedduring the TDD transmission time-slot. For example, the remote units 102a-d can include TX/RX controllers 306, 406, 506 that can increase thegain of the downlink resource block. In one example, the TX/RXcontrollers can send commands to signal conditioners that performdigital signal processing on the downlink radio blocks to increase thepower envelope of the sub-frames in the downlink radio blocks. Inanother example, TX/RX controllers can send commands to adjust the gainson a per-slot basis. In a further aspect, TX/RX controllers can directlyperform digital signal processing on the downlink radio block toincrease the gain.

In block 608, an uplink gain of an uplink gain is reduced during the TDDtransmission time-slot. For example, TX/RX controllers can reduce thegain of the uplink radio blocks by sending commands to coupled signalconditioners to perform digital signal processing on the uplink radioblocks. Similar to the downlink radio blocks, the signal conditionerscan reduce the gain of the uplink radio blocks by reducing the powerenvelope of the sub-frames in the uplink radio blocks or adjust thegains on a per-slot basis. By reducing the gain of the uplink radioblocks during a TDD transmission time-slot, the process can protect theuplink communications path from being overdriven by the strong transmitsignals being sent on the downlink communications path.

While the present subject matter has been described in detail withrespect to specific aspects and features thereof, it will be appreciatedthat those skilled in the art, upon attaining an understanding of theforegoing may readily produce alterations to, variations of, andequivalents to such aspects and features. Accordingly, it should beunderstood that the present disclosure has been presented for purposesof example rather than limitation, and does not preclude inclusion ofsuch modifications, variations and/or additions to the present subjectmatter as would be readily apparent to one of ordinary skill in the art.

What is claimed is:
 1. A distributed antenna system, comprising: ahead-end unit including a time-division duplexing (“TDD”) mode schedulerconfigured to identify a start of a downlink radio block that includesfrequency-division duplexing signals based on monitoring a downlinkcommunications channel and generate an indication of a TDD transmissiontime-slot based on the start of the downlink radio block; and a remoteunit configured to receive an uplink radio block on an uplinkcommunications channel and transmit the downlink radio block on thedownlink communications channel, the remote unit including atransmit/receive controller configured to receive the indication of theTDD transmission time-slot, increase a downlink gain of the downlinkradio block during the TDD transmission time-slot, and reduce an uplinkgain of the uplink radio block during the TDD transmission time-slot. 2.The distributed antenna system of claim 1, wherein the TDD modescheduler is further configured to generate an indication of uplinkactivity by monitoring the uplink communications channel, wherein thetransmit/receive controller is further configured to receive theindication of uplink activity, increase the downlink gain of thedownlink radio block based on the indication of uplink activity, andreduce the uplink gain of the uplink radio block based on the indicationof uplink activity.
 3. The distributed antenna system of claim 1,wherein the transmit/receive controller is configured to increase thedownlink gain by increasing a power envelope of a transmit sub-frame. 4.The distributed antenna system of claim 1, wherein the transmit/receivecontroller is configured to increase the downlink gain by increasinggains of resource slots included in the downlink radio block.
 5. Thedistributed antenna system of claim 1, wherein the transmit/receivecontroller is further configured to determine an isolation measurementbetween the uplink communications channel and the downlinkcommunications channel, determine an amount of uplink gain reductionbased on the isolation measurement, and reduce a gain of the uplinkcommunications channel based on the amount of uplink gain reduction. 6.The distributed antenna system of claim 5, wherein the transmit/receivecontroller is configured to determine the isolation measurement betweenthe uplink communications channel and the downlink communicationschannel by calculating an amount of power transmitted on the downlinkcommunications channel that is received on the uplink communicationschannel.
 7. The distributed antenna system of claim 1, wherein theremote unit further comprises a transmit antenna and a receive antenna,wherein the transmit antenna and the receive antenna are physicallyseparated from each other.
 8. A unit of a repeater system, comprising: atransmitter configured to transmit a downlink radio block that includesdownlink frequency-division duplexing signals on a downlinkcommunications channel; a receiver configured to receive an uplink radioblock that includes uplink frequency-division duplexing signals on anuplink communications channel; a time-division duplexing (“TDD”) modescheduler configured to identify a start of the downlink radio blockbased on monitoring the downlink communications channel and generate anindication of a TDD transmission time-slot based on the start of thedownlink radio block; and a transmit/receive controller configured toreceive the indication of the TDD transmission time-slot, increase adownlink gain of the downlink radio block during the TDD transmissiontime-slot, and reduce an uplink gain of the uplink radio block duringthe TDD transmission time-slot.
 9. The unit of claim 8, wherein the TDDmode scheduler is further configured to generate an indication of uplinkactivity by monitoring the uplink communications channel, wherein thetransmit/receive controller is further configured to receive theindication of uplink activity, increase the downlink gain of thedownlink radio block based on the indication of uplink activity, andreduce the uplink gain of the uplink radio block based on the indicationof uplink activity.
 10. The unit of claim 8, wherein thetransmit/receive controller is configured to increase the downlink gainby increasing a power envelope of a transmit sub-frame.
 11. The unit ofclaim 8, wherein the transmit/receive controller is configured toincrease the downlink gain by increasing a gain of resource slotsincluded in the downlink radio block.
 12. The unit of claim 8, whereinthe transmit/receive controller is further configured to determine anisolation measurement between the uplink communications channel and thedownlink communications channel, determine an amount of uplink gainreduction based on the isolation measurement, and reduce a gain of theuplink communications channel based on the amount of uplink gainreduction.
 13. The unit of claim 12, wherein the transmit/receivecontroller is configured to determine the isolation measurement betweenthe uplink communications channel and the downlink communicationschannel by calculating an amount of power transmitted on the downlinkcommunications channel that is received on the uplink communicationschannel.
 14. The unit of claim 8, wherein a shared transmit/receiveantenna includes the transmitter and the receiver.
 15. A method,comprising: monitoring a downlink communications channel in whichinformation formatted in radio blocks that include frequency-divisionduplexing signals is communicated; identifying, based on the downlinkcommunications channel, a start of a downlink radio block; based on thestart of the downlink radio block, generating an indication of atime-division duplexing (“TDD”) transmission time-slot; increasing adownlink gain of the downlink radio block during the TDD transmissiontime-slot; and reducing an uplink gain of an uplink radio block duringthe TDD transmission time-slot.
 16. The method of claim 15, furthercomprising: monitoring an uplink communications channel for anindication of uplink activity; increasing the downlink gain of thedownlink radio block based on the indication of uplink activity; andreducing the uplink gain of the uplink radio block based on theindication of uplink activity.
 17. The method of claim 15, wherein atransmit/receive controller is configured to increase the downlink gainby increasing a power envelope of a transmit sub-frame.
 18. The methodof claim 15, wherein a transmit/receive controller is configured toincrease the downlink gain by increasing a gain of resource slotsincluded in the downlink radio block.
 19. The method of claim 15,further comprising: determining an isolation measurement between anuplink communications channel and the downlink communications channel;determining an amount of uplink gain reduction based on the isolationmeasurement; and reducing a gain of the uplink communications channelbased on the amount of uplink gain reduction.
 20. The method of claim19, wherein the isolation measurement between the uplink communicationschannel and the downlink communications channel is determined bycalculating an amount of power transmitted on the downlinkcommunications channel that is received on the uplink communicationschannel.